localized predominantly within spherical vesicular structures that range from 0.0002-0.0006 mm in diameter, located in the cytoplasm and within the central vacuole in differentiated cotyledon cells. The N-terminal region, including the transmembrane domain of HMGR, is found to be necessary and sufficient for directing HMGR to the endoplasmic reticulum and the spherical structures

the enzyme spans the endoplasmic reticulum membrane twice. Both the N-terminal region and the highly conserved catalytic domain are in the cytosol, whereas only a short stretch of the protein is in the endoplasmic reticulum lumen. Insertion in the endoplasmic reticulum membrane is mediated by the signal recognition particle (SRP) that recognizes the two hydrophobic sequences which will become membrane spanning segments